The threat to British shipping from German U-boats remains high. In an effort to combat this, the Admiralty has commissioned North Sea Class airships to escort convoys in the North Sea. These ships are much bigger than the existing Submarine Scout Airships and should be able to stay in the air for a minimum of 20 hours.
Approval was given in January 1916 for the construction of six NS class airships; designed and built at RNAS Kingsnorth. The design was similar to the Coastal Class airships being a tri-lobe envelope based on the Astra-Torres design principles. The envelope had a capacity of 360,000 cubic feet (10,000 m3. The airship was 260 feet long. Attached to the envelope were four fins. The smaller top fin was merely for stabilizing purposes; while the larger other three were identical in size and shape, and carried the rudder and elevators. The aluminium fuel tanks were initially situated above the top ridges of the envelope, but later placed inside the envelope.
The prototype ship NS1 underwent trials at Kingsnorth in February 1917. The ship was transferred on 18 April to the air station at Pulham for further operational tests. In retrospect this was a mistake as many of the problems that initially beset the aircraft could have been avoided had more extensive tests been carried out at Kingsnorth
In service the original NS ships proved disappointing. This was primarily due to the complicated transmission gear which was used to transfer power from the Rolls Royce engines to the propellers. This was partly caused by the fact that the engines were originally designed for cars. The second issue was that the crew gondola was not very streamlined and the control car and engine car were separated.
These problems were eventually solved by replacing the Rolls Royce engines with lighter Fiat engines with direct drive. The cabin was also redesigned into a single unit. This made the aircraft lighter and more streamlined and therefore more efficient and faster. The ships eventually set various records for non-rigid airships.